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Old 11-14-2009, 09:47 PM   #1
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Default Hydrometer Reading Question

If I leave my hydrometer in the tube with the sample for like 15 min it seems to rise. Is it just because the temp is changing?

So I pull a sample out of 68F take an FG and I get 1.008.

After about 15-20 min, when I finished bottling the hdrometer in the tube is reading 1.012 ... I'm sure the temp went up but only to like 72-73F...

What is my real FG?

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Old 11-14-2009, 09:54 PM   #2
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It may be moving due to CO2 coming out of suspension. There is more in suspension when you first pull the sample. After 15-20 min, there is less, which will give a different reading. The 4-5 degree change would'nt move your reading that much.

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Old 11-14-2009, 09:55 PM   #3
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Always swirl/spin your hydrometer right before taking a reading.

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Old 11-14-2009, 10:17 PM   #4
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The closer the liquid line is to the top of the test tube, the easier it is to get an accurate reading. I've marked my test tube with a sharpie to give me an idea of where the liquid should come to before I drop in the hydrometer.

Try and get the hydrometer to float free of the sides of the test tube. Spinning the hydrometer before taking a reading knocks off bubbles so that the reading is more accurate.

Good Luck...

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Old 11-15-2009, 12:30 AM   #5
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I did/do all that, but I've never left the thing in the tube for this long. You should take a reading right after you pull the sample, right?

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Old 11-15-2009, 12:31 AM   #6
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Default Great Tip on the full tube!

Thanks for that tip, I'll 'calibrate' my liquid so when I drop it comes nearest the top.

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Old 11-15-2009, 02:21 PM   #7
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It's takes more shaking than you'd think to completely de-gas a sample. Bubbles are a big problem with a finish hydrometer, so I shake a sample 60 seconds and let it stand for a couple minutes.

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Old 11-15-2009, 05:08 PM   #8
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Cool so the 'final reading of 1.012 was probably more accurate than the 1.008 - makes sense too..

Thanks

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Old 11-16-2009, 04:21 PM   #9
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Out of curiosity, how do bubbles affect the reading? On one hand, I understand the idea that, once the gas it out, you have more density, so you will theoretically get a higher gravity reading. On the other hand, if you take a reading while the sample is degassing, wouldn't that make the hydrometer more buoyant and therefore read "higher" when, in fact, it should be a lower SG?

For example, I take a hydrometer reading while I see some bubbles degassing from the sample. It reads 1.02. Since I am taking the reading during the degasssing, should I assume the SG is lower, say, 1.018 or so?

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Old 11-16-2009, 04:39 PM   #10
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Good q, my FG went up after 10 min from 1.008 to 1.012 - if gas left wouldn't the hdrometer be less bouyant? Good q!

I've seen people using those Brix meters (refractometers) are they much better?

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